1. Field of the Invention
The present invention relates to a power supply circuit which can change its stabilized output voltage, in steps in response to an external control signal.
A power supply circuit in accordance with the present invention can be used, for example, for changing the voltage level applied to microwave amplifiers to change the amplification degree and for cutting off or restoring the stabilized output voltage applied to microwave amplifiers.
2. Description of the Prior Art
Stabilizing power supply circuits are used for a wide range of applications. In microwave applications, two stepped stabilized power supplies are required. The first power supply is used for changing the amplification of a microwave amplifier, to detect a malfunction in another microwave amplifier being operated in parallel. The second power supply is used for cutting off the stabilized power supply to a microwave amplifier when the amplifier is in an abnormal state and restoring the power supply when the amplifier returns to normal.
There are several ways to provide these two stabilized power supplies. A first approach is to provide two circuits, one having a higher output voltage and the other having a lower output voltage. As can be easily understood, this has the disadvantages of higher manufacturing cost, greater size, and requiring for a complicated switching circuit.
A second approach is to install parallel resistors in the circuit and switch these resistors in response to external conditions. This approach, however, has the disadvantages of a slight loss of stability in the output voltage during transition and the need for a complicated switching circuit.
A third approach is to use a variable resistor in the circuit and to vary the resistance by a manual or automatic changing device. However, this results in more complex operation and may entail the use of a complex device when automatic changing is desired.